What deadlines should high school seniors be aware of in 2023-24?

CSS Profile opens 10/1, as usual. Filing deadlines are specific to college and round of admission

Likewise, FAFSA deadlines are college/round of admission specific, even though FAFSA won’t be available until December.

Also, although technically the final FAFSA deadline is June 30, if one wants a financial aid package in a timely manner they have to make each school’s FAFSA deadline for the round the student applied.

List first choice school for NMF status - typically March - May 31 (again, college specific)

Note that February is misspelled in a few places in the original post.